Desulfurization of zinc sulfid ores



GILBERT RIGG, OF MELBOURNE, VICTORIA, AUSTRALIA, ASSIGNOR TO MINING AND ,METALLURGICAL PROCESSES PROPRIETARY LIMITED, OE MELBOURNE, VICTORIA,

AUSTRALIA.

DESULFUBIZATION OF ZINC SULFID ORES.

I'o Drawing. Application filed May 21,

-T 0 all whom it may concern Be it known that I, GILBERT Rico, metallurgist, a subject of the King of Great Britain, residing at Melbourne, in the State of Victoria, Commonwealth of Australia, have invented certain new and useful Improvements in the Desulfurization of Zinc Sulfid Ores, of which the following is a specification.

This invention relates to certain improvements in the desulfurizing of zinc sulfid ores and refers more especially to the desul-- furizing of blende concentrates (both granular material and slimes) preparatory to the recovery of -metallic zinc or spelter therefrom by distillation or leachin for electrodeposition or the production 0 zinc oxid.

Hitherto the desulfurization of zinc'sulfids has been effected by roasting in reverberatory or muflle furnaces with more or less continuous rabbling either by hand or mechanical means for the purpose of maintaining the ore particles as far as possible; in contact with the oxidizing atmosphere and for the elimination of sulfur dioxidgases occluded in the ore.

In order to effectively desulfurize zinc sulfid ores it has beenfound necessary hitherto to first crush the ore to such a size as will pass through from 8 to 20 mesh per linear inch according to the character of the ore.

When the ore to be treated has been previously concentrated, as for instance by gravity or flotation, it is usually in a still ner state of division. This fine condition of the ore While necessary for the roasting has serious drawbacks when the ore is submitted to reduction and distillation in retorts. In the first place it interferes seriously with the transmission of heat from the walls of the retorts to the body of the charge while further there is a greater tendency to fuse with the formation of slag. As is well known in retort practice it is desirable to eliminate slagging as far as possible both on account of the destructive effect of the slag u on the retorts and also on account of the dii culty of drawing partly slagged residues from the retorts. Again the fineness of the charge retards the reduction of the metal within the retorts by hindering the free circulation of carbon monoxid gas formed within the retorts which, as it comes into contact with the particles of zinc oxid Specification of Letters Patent. Patented D66. 27, 1921.

1918. Serial No. 235,784.

roasting or desulfurizing operation have.

been found to have an outer coating of zinc oxid with a substantial kernel or core ofunaltered sulfid. Such partially roasted ore has-been found to give very poor results in the retort with in many cases a highly destructive action on the clays of which the retorts are composed. Furthermore zinc blende which has been submitted to a pre-.

vious treatment by gravity concentration or flotation, usually comes to thesmelter in a much finer state of subdivisioni Attempts have been made to briquet the ore with coal or other carbonaceous fuel before charging the same into the retorts but such briqueting operations have not up to the present been successful. If the briquets-are suiii-ciently compressed to insure them not crumbling in the retorts they are too compact to enable them to work quickly, while if they crumble the advantage of briqueting is nullified.

Blende ores have not hitherto been amenable to, blast roastingthat is by causing a current of air to pass through a body or bed of the ore which was previously ignitedowing to the excessive heat generated causing fusion and preventing-contact between the ore particles and the oxidizing atmosphere.

The object of this invention is to rovide certain improvements in the desulf firizing of zinc sulfid ores whereby the elimination of the sulfur may be effected more economically and effectively than heretofore yielding-a product of roasted or desulfurized ore a in coarse grained form in lumps of a porous nature and in a form suitable for reduction in distillation retorts and for leaching for elecro-deposition and the production of zinc 0x1 I accomplish this object by effecting the 1110 desulfurizing of blends ores in two separate operations the first of which comprises a partial roast for the dilution of the sulfur contents and the second of which consists I of subjecting the said partially roasted ore to a blast roasting operation that is to say igniting the charge and causing a current of air or oxidizing atmosphere to pass through the ore whereby the combustion of the sulfur is maintained and the ore finally desulfurized. and a product obtained in theore is delivered on to the surface of traveling grates which pass beneath an ignition burner after which the said grates travel over a suction chamber whereby air is drawn through the bedof ore. It will, however, be understood that the purpose of the invention may be efiectedby employing other forms of blast roasters in which a current of air or oxidizing atmosphere isl blown or drawn through a charge vbrl, bed of'ore on a perforated grateand it willberunderstood that in this specification the term' Blast roaster or its'equivalent will include'alllsuchtypes of apparatus. I I.

For the purpose of this invention it is essential that the sulfur contents of the ore should be reduced in the first operation to such an ertentthatthe heat generated in the second or blast roasting operation will not be sufiicient to cause fusing "or slagging. Such reduction of the sulfur contents may be effected in several ways, such as,

(1) By partially roasting the ore until the sulfur contents are reduced; to say from 8 to 10% and thensubjec'ting the said partially roasted ore to blast roasting.

(2) By partially roasting a certain ortion of the ore and mixing such part1ally roasted ore with green or unroasted ore in such proportions that the mixture has a sulfur content of say 8 to 10% and then subjecting such mixture to blast'roasting.

(3) By more or less completely roasting or desulfurizing the ore (such as to a dead roast) and mixing such desulfurized ore with; green or unroasted ore in such proportions that the mixturehas a'sulfur content ofsay from 8% to 10% andthen' subjecting such mixture to blast roasting.

In some cases/ll may eflect the purpose of this invention by subjecting the ore to a preliminary roast in a reverberatory or muflie or other suitable furnace for the elimination of part of the sulfur and subjecting such partially roasted ores to blast roast ing in which air or oxidizing. atmosphere neonvee is drawn or forced through the charge. In the working of such a'method the most economical arrangement would be to work each type of roaster between its most efiective limits and for this purpose I prefer to use a multiple hearth roaster and conduct the operations therein sothat the ore is reduced down to about 8 to l0% sulfur. Reducing the ore to about 8 to 10% sulfur is, however, merely illustrative, as the actual percentage is dependent on the particular ore treate the invention residing rather in the result than in the actual percentage of sulfur removed. This artially roasted'ore with or without dampmg as may be necessary is then fed on to the grate of a blast roaster the desulfurized ore being in the form of a 'sinter suitable for subsequent treatment for the recovery of the zinc or the production of zinc oxid.

In many cases after a preliminary roast in the reverberatory furnace or mufile furnace as above indicated it is found that the ore contains a certain proportion of grains which have ,an external coating of zinc oxid surrounding the internal kernel or core of unaltered sulfid; This condition tends. to interfere with the rapid ignition of the charge in the, blast roaster; l have found that this condition may be overcome byad-ding to the ore coming from the aforesaid'preliminary roast or desulfurization a small proportion of unroa's ed or green sulfids. This unroasted ore not having any inert coating rapidly ignites and helps to bring up the temperature to a point at which roasting and sintering of the ore proceeds at a satisfactory rate. I

lln practice the proportion or quantity of roasted ore to the green sulfids is estimated according to the amount required to avoid fusing of the ore particles in the subsequent treatment.

For example in the treatment of Broken Hill zinc sulfid ores it has been found that an ore roasted to 8% sulfur in a preliminary desulfurization when mixed with an addition of raw sulfid ore to bring the su fur contents up to 10% gives a very satisfactory desulfurization and sintering in the blast roaster.

The sintered mass is then broken into comparatively coarse lumps such for example as will pass through a half inch screen the coarseness of the grain being to some extent determined by the charactervof the sinter. This roasted or de'sulfurized prodnot in the form of relatively coarse and porous pieces is then mixed with coal and charged into the distillation retorts in the ordinary Way when the reduction takes place with ease and rapidity it being found that a reduced amount of fuel is necessary for the reduction while the retort yield is increased and in all respects the advantages roasting furnace.

are obtained which would be expected to accrue from the use of a coarsely divided ore being at the same time sufliciently porous for the passage of the reducing gases.

It has been found desirable to use a bind-' l mixed with water form a more or l ess plastic mass which acts as a most effective binder for the sulfids on the grates of the blast roaster besides providing the necessary amount of greensulfids for admixture with the pro-roasted ore. By damping the pm-roasted ore with a mixture ofwater and these slime concentrates and then subjecting the same to-ignition and blastroasting the difficulty of blow holes can be overcome and the dust losses reduced to a minimum. When slimes are not available plastic clay may be used in the same way with good results.

The temperature resulting from the combustion of the sulfur may be further controlled in the blast roaster by mixing with the' air oratmosphere being drawn or forced through the ignited body" of ore a certain proportion of steam or water vapor. The proportion of steam to the air or oxidizing atmosphere is determined according to the amount necessary to avoid the generation of heat sufficient to fuse and slag the particles. I 1

When it is desirable to utilize sulfur dioxid gases obtained by the desulfurizing or roasting of the ores for the purpose of manufacture of sulfuric acid it may be found that by this method of treatment the gases coming from the final roast or desulfurization on the blast roaster are not sufficientlyrich in sulfur dioxid for economical'manufacture of acid. In such cases the aforesaid gases may be enriched by drawing the gases or a portion of the gases from the blast roaster and passing them over one or more hearths of the preliminary In this way the gases may be enriched as to their sulfur dioxid contents and thereby be of suificient strength for manufacture of sulfuric acid.

In practice it is found that ore treated in this way may be desulfurized to such an extent as is necessary for all practical purposes and that the resultant sintered mass is in a fine porous condition which may be easil broken and is found to be in avvery suita 1e condition for treatment in retorts fordistillation of spelter or for leaching preparatory to electro-deposition or the production' of zinc oxid.

1 claimv 1. In theart of roasting zinc sulfid ores the process which consists in subjecting the ore to a preliminary roast and then subjecting to a blast roast, the preliminary roast eliminating sulfur to such a degree that the blast roast produces a porous sinter.

2. The desulfurizing of zinc sulfid ores (blende) characterized by the production of a roasted product in coarse grained form and intimately porous in which form it is peculiarly suited to treatment in the distillation process, said desulfurizing being effected in two separate operations, which comprise first subjecting the ore to a preparatory roasting for the dilution of the sulfur contents to such an extent that fusion and slagging are avoided in the subsequent blast roasting operation, the said preparatory roasting leaving the ore in a fine granular condition, "and then blast-roasting the said ore for the further elimination of sulfur and until a sinteredvproduct is formed of a relatively coarse and porous character the porosity of the sintered product thus obtained being sufiicient for the free passage of the gases generated inzinc distillation retorts.

3. In the desulfurizing of zinc sulfid ores first subjecting the ore to a partial roast for the dilution of the sulfur contents then mixing such partially roasted ore with green or unroasted zinc sulfids in proportions that the sulfur contents of the mixture are such that fusion and slagging are avoided in the subsequent operation and subjecting the mixture to a blast. roasting operation for the elimination of the sulfur and the formation of a sintered product.

4. In the desulfurizing of zinc sulfid ores subjecting the ore to a more or less complete roast (such as a dead roast) mixing such roasted ore with green or unroasted zinc sulfids in proportions that the sulfur contents of'the mixture are such that fusionand slagging are avoided in the subsequent operation and then subjecting the mixture to a blast roasting operation for the elimination of the sulfur and the formation of asintered product substantially as described.

5. In the desulfurizing of zinc sulfidores first subjecting the ore to a partial roast then mixing such partially roasted ores with water containing green zinc sulfid slimes in proportion that the sulfur contents of-the mixture are such that fusion is avoided in the subsequent operation subjecting the mixture to a blast roasting operation for the elimination of the sulfur and the formation of a sintered product substantially as described.

6. In the desulfurizing of zinc sulfid ores first subjecting the ore to a partial roast then mixing such partially roasted ore with a certain proportion of green sulfids moistening the mixture with a binding agent and subjecting the mlxture toa blast roasting operation for the elimination of the sulfur and the formation of a sintered product substantially as described.

7 In the desulfurizing of zinc sulfid ores first subjecting the ore to a partial roast, said partial roast leaving it in a fine grained condition, adding a binding agent to the partially roasted ore said binding agent being of a character which will be effective below the sintering temperature of the charge to prevent the finely-divided particles from running through the grate of the subsequently employed blast roaster or from thereafter forming blow holes thereon, and finally subjecting the charge to a blast roastin operation for the further elimination of sulfur and the formation of a sintered product of a relatively coarse and porous character; substantially as described.

8. In the desulfurizing of zinc sulfid ores first subjecting the ore to a partial roast then mixing such partially roasted ores with a certain proportion of green or unroasted zinc sulfids, moistening the mixture With water containing green or unroasted zinc sulfid slimes and subjecting the mixture to a blast roasting operation for the elimination of the sulfur and the formation of a sintered product substantially as described.

9. In the desulfurizing of zinc sulfid ores first subjecting the ore to a partial roast then mixing such partially roasted ores with a certain proportion of green or unroasted zinc sulfids, moistening the mixture with water containing clay and subjecting the mixture to a blast roasting operation for the elimination of the sulfur and the formation of a sintered product substantially as described.

10. In the desulfurizing of zinc sulfid ores (blende) first partiall roasting the ore for the dilution of the sul ur contents then mixing such partially roasted ore with green. or unroasted zinc sulfids and then subjecting the mixture to a blast roasting operation introducing steam or water vapor with the air being drawn or forced through the ignited body of ore in such proportions as may be necessary to avoid fusing and slagging whereby the elimination of the sulfur is effected with the formation of a sintered product substantially as described.

In testimony whereof l have affixed my signature in presence of two witnesses.

GILBERT RIGG.

Witnesses ANNA HAQK, G. B. Curran. 

